Hydrothermal vents as indicators of Earth's core changes

Hydrothermal Vents: A New Way to Monitor the Earth's Core

Deep sea-thermal vents are an important part of life on our planet. These unique areas of the ocean provide an oasis for life on the sea floor that are supported by thermal and chemical processes situated deep in the earth's interior. It is thought that life on earth may have begun in one of these life giving deposits of biological activity. The following will explore hydrothermal vents and their contribution to the many biological beings that make these extreme conditions their home. It will support the thesis that by examining their reactions to continuously changing conditions in their environment we can gain clues as to changes that are occurring in the Earth's core.

What Are Hydrothermal Vents?

Hydrothermal vents are found in some of the deepest places in the ocean, far beyond the reach of normal submarines or divers. The closest analogy is to geysers on land. A hydrothermal vent is nothing more than a geyser that occurs on the ocean floor. It occurs when two oceanic plates pull apart and the erupting lava spews out onto the sea floor, creating a volcano-like structure. As hot fluid Flows into the very cold water it cools down quickly. The cold minerals settle around the vent opening and create chimney formation. Some of these chimneys can be quite tall, as high as 6 kilometers in some places (ONR 2006).

For the most part, the ocean floor is a sparsely inhabited area of the planet. However, hydrothermal vents are teeming with life. Hydrothermal vents are home to some extremely fascinating creatures to such as tube worms, giant clams, eyeless shrimp and spider crabs (ONR 2006). Cold seeps are other areas that are similar to hydrothermal vents, but the waters in them are closer to the temperature of the surrounding waters. Cold seeps support a similar array of life. Life around these geothermal fountains is dependent upon the chemicals in the surrounding water. The most common chemicals in the water include hydrogen sulfide, methane, iron, manganese, and silica (ONR 2006). This creates an extremely harsh environment to support life.

Hydrothermal vents are typically only active for one or two years. However, during their brief lifespan they support an abundance of life. There are nearly 300 species that live around these fleeting habitats (ONR 2006). These creatures live in a world of darkness as sunlight cannot penetrate to these depths. Plants at these depths do not depend on photosynthesis as the basis of the food chain. Chemosynthesis is the basis of life around vent areas. This food chain is similar to terrestrial food chains where larger animals prey on smaller ones. The most simplistic life form, and consequently the bottom of the food chain, is chemosynthetic bacteria. Larger animals eat the bacteria and the bacteria continue to live inside of their body. Some animals, such as tube worms, do not have a mouth or a digestive tract. They depend on the bacteria that live inside their bodies to provide nutrients directly to the organism's tissues (ONR 2006).

Life in an Alien World

Life at the vents is dynamic and constantly changing. From one small area to the next conditions can change dramatically. Yet, a number of simple creatures have learned to carve out their existence in the microhabitats around vents. The diversity of life around the vents is surprising, with nearly 300 species identified thus far (Herring 2006). The number and types of species found around hydrothermal vents give us clues as to the chemical constituents and processes that take place in and around them. One process that has allowed creatures to survive in what would be inhospitable to other creatures is the development of symbiotic relationships. These relationships help fill the gaps where one species could not survive because it lacked something that it needed to live in that particular area. Many times, if the creature cannot produce the chemicals or the processes that it needs, it will enlist the help of another sea creature to provide what it is missing. Both animals get something that they need to survive. One of the more common symbioses to develop is between invertebrates such as tube worms and chemosynthetic bacteria (Dechaine and Cavanaugh 2006). The development of symbiotic creatures is known as co-speciation. This means that in order for these creatures to develop both of them had to evolve simultaneously.

A considerable amount of academic energy has been spent classifying the flora and fauna of hydrothermal vents communities. A majority of academic research found in journals has to do with the classification of various hydrothermal vent communities. Classifying species from this unique environment can be complicated because the lines between plant and animal are not as clearly distinguishable as with terrestrial species. Tarasov and associates (2005) divided hydrothermal vents into deep and shallow water environments. They found that plant species change drastically when one approaches 200 meters in depth. Deep-sea valley communities are different than surface communities. They can be distinguished by their lack of diatoms and algae mats (Tarasov et al. 2005). Algae require light to form. There is also a significant decrease in the phytoplankton population. At this break in depth one begins to see large sulfide structures that are not present near the surface (Tarasov et al. 2005). The rules for deep-sea life are different than those for terrestrial species. Stratification plays an important role in species classification in vent environments. As the chimney grows in height the environment changes.

Tarasov and associates believe that deep-sea vents have a longer evolutionary history then shallow vents found closer to the surface. This is an important factor in understanding how hydrothermal vents are connected to early life on planet earth. Deep-sea hydrothermal vent communities represent a different phenomenon than shallow water vents. The chemical processes that take place in the deep-sea vent communities are very different from those in shallow areas. Shallow vent species receive light from the sun and more closely resemble terrestrial life forms. However, this is not so with deep-sea forms. Hydrothermal plumes are a rising column of hot water that can have sharp definitions in microhabitats. Similar species found inside the plume and outside of the plume can be distinguished as being different from one another (Nakagawa, Takai, and Fumio 2005). Govenar and associates (2005) found that changes in species could signal changes in vent temperature and other conditions. Studying these phenomenons could have significant implications for study of the earth's core and monitoring temperature fluctuations that could be associated with volcanoes or other tectonic phenomenon. Monitoring species near hydrothermal vents could lead to a new method for monitoring the Earth's core.

The conditions under which many vent species exist are precarious to say the least. A certain crab species that lives in the high sulphur vents in the shallow waters off Taiwan had to develop an interesting adaptation in order to feed. These crabs live an environment that is low in nutrients. Their natural diet consists of zooplankton. In order to survive the crabs had to learn to eat the zooplankton that falls like snow on to the sea floor. The zooplanktons that comprise the diet of these crabs were killed when they got too close to the sulfurous plumes of the vent (Jeng, Ng, and Ng 2004). The crabs simply clean up the debris.

Many species that live within the hypodermic vent area must exist within a very narrow range of temperature, pH, and chemical content of the water. One of the more interesting topics concerning these species is how a particular species can inhabit two different vents. Ocean currents and the topography of the ocean floor play a major role in the dispersal of creatures. It has been found that in some areas the topography of the floor itself may be a limiting factor in the ability of species to travel from one vent to another (Thompson et al. 2003). Due to the narrow habitat in which these creatures can survive, many times a creature will be transported to an environment where it will not be able to live. However, in some cases the species may be able to adapt to the new area. The species will have a major impact on the natural habitat that already exists in the area. They will represent a new predator in new prey for other species. They may also introduce new chemical processes to the vent system.

Hot springs on the sea floor and on land may be some of the oldest populated habitats on earth. The interactions between water in the rock surrounding the vent provide a variety of energy sources to sustain life (Reysenbach and Shock 2002). Changes in these micro environments also give us clues that changes are going on within the earth's core. As a micro environment begins to shift species must learn to adapt to these changes or die. For instance, a die off of one species could mean that drastic changes have occurred in one of the essential conditions necessary for that specie's survival. Levels of various species would also give as clues as to environmental changes as well. These habitats could do more than simply give us clues about the beginnings of life on earth. They can give us clues as to the internal workings of the earth itself.

Five biogeographic regions are recognized on the ocean floor. Exploring evolutionary similarities and differences in the flora and fauna at the vents tells us about the specific conditions that exist within that area (Van Dover, Humphris, and Fornari 2001). Biology in these areas can tell us much more about geology than was once thought. For instance, let us consider the larval stage of the giant tube worm. The larval stage of the giant to worm is around 38 days. The dispersal of these creatures can tell us about flow patterns and around the ocean floor's hypodermic vents (Marsh, Mullineaux, Young and Manahan, 2001). Marsh and associates found that these tube worms on the East Pacific Rise rarely exceeded distance of 100km. Tube Worms are dependent upon ocean floor currents to disperse their larva. Reversals and unique flow patterns along the ridge were found by tracking larva dispersal. The lifespan of these larva and many other creatures can now be used to study ocean currents at and between different hydrothermal vents on the ocean floor.

In conclusion, life at hydrothermal vents is precarious and dynamic. A life-giving vent may suddenly appear or disappear. Life in hydrothermal vents gives us a glimpse of how the first life-forms may have evolved on earth. However, recent attention has been directed towards discovering what these species can tell us about their environment. This important paradigm shift changes the way we have traditionally viewed the relationship between biology and geology. Life around hydrothermal vents can give us many clues about changing tectonic conditions within the earth's core.